This invention relates to an electronic musical instrument, more particularly an improvement of an electronic musical instrument wherein tone production channel of the number smaller than that of the keys of a keyboard are provided for assigning a depressed key to either one of the tone production channels for producing a musical tone.
Recently, for the purpose of decreasing manufacturing cost by simplifying the wiring of the keyboard, by utilizing LSIs for constructing the circuit and by reducing the number of tone source circuits it has been developed an electronic musical instrument in which tone production channels of the number much smaller than the number of keys are provided so as to assign only a depressed key or keys to either one or more of the tone production channels for producing musical tones. In an electronic musical instrument provided with an upper keyboard generally used for melody performance and a lower keyboard generally used for accompaniment, usually the upper keyboard tone and the lower keyboard tone have different tone properties including tone color and amplitude envelope. For this reason, it is necessary to independently provide a plurality of tone production channels for the upper keyboard and a plurality of tone production channels for the lower keyboard. An electronic musical instrument of this type is disclosed in, for example, U.S. Pat. No. 4,192,211 issued on May 11, 1980 to Eiichi Yamaga et al. In this type of instrument, it is necessary to provide the tone production channels respectively for the upper and lower keyboards of the number sufficient to produce simultaneously a maximum number of tones, for example about 10. This is because in some cases, only the upper keyboard must be performed with both hands, or only the lower keyboard must be performed with both hands. However in a normal mode of performance utilizing both upper and lower keyboards, a melody performance is performed by utilizing the upper keyboard with one hand (right hand) and an accompaniment performance is performed by utilizing the lower keyboard with the other hand (left hand). In this case, the number of the actually used tone production channels (about 1 to 3 channels) for respective upper and lower keyboards is much smaller than the total number of the tone production channels leaving many channels idle.